System Function DL

⎕DL or system function Quad DL is available in monadic form only.

Monadic Function

Z←⎕DL R Delays APL program execution / pauses APL processing for the number of seconds specified in R. R should be a real number (representing seconds and it is not necessary for R to be a whole integer) and R should be greater than zero.

R is - normally a number greater than zero.

Z returned by APL's interpreter - is a scalar number, showing exactly how many actual seconds APL was delayed and Z's value is normally somewhat close to input R's value.

Monadic system function ⎕DL is similar to a sleep or thread sleep routine in other languages.

The following pauses NARS APL program execution for roughly greater than six and a half seconds:

      ⎕DL 6.651 
6.646 

R was 6.651 (user specified). Z returned was 6.646. This system function is useful where concurrent/simultaneous processes are running or APL may be dependent on an external routine/program which is running and that external routine needs to finish first, so for example APL can read in the external results. If ⎕DL is used in a user function, say within a loop, every R seconds your APL function can check for that external result, e.g. existence of a file, value within that file, etc.

System Variables (A value may be assigned to these except for ⎕DM)
⎕ALX	⎕CT	⎕DM	⎕DT	⎕ELX	⎕FC	⎕FEATURE	⎕FPC	⎕IC	⎕IO
⎕LR	⎕LX	⎕PP	⎕PR	⎕PW	⎕RL	⎕SA	⎕WSID
Niladic System Functions (a value cannot be assigned to these)
⎕A	⎕AV	⎕EM	⎕ET	⎕LC	⎕NNAMES	⎕NNUMS	⎕SI	⎕SYSID	⎕SYSVER
⎕T	⎕TC	⎕TCBEL	⎕TCBS	⎕TCESC	⎕TCFF	⎕TCHT	⎕TCLF	⎕TCNL	⎕TCNUL
⎕TS	⎕WA
Monadic or dyadic system functions (a value cannot be assigned to these)
⎕AT	⎕CR	⎕DC	⎕DFT	⎕DL	⎕DR	⎕EA	⎕EC	⎕ERROR	⎕ES
⎕EX	⎕FMT	⎕FX	⎕MF	⎕NAPPEND	⎕NC	⎕NCREATE	⎕NERASE	⎕NINFO	⎕NL
⎕NLOCK	⎕NREAD	⎕NRENAME	⎕NREPLACE	⎕NRESIZE	⎕NSIZE	⎕NTIE	⎕NUNTIE	⎕STOP	⎕TF
⎕TRACE	⎕UCS	⎕VR
Note that quad functions and variables (except for the ⎕A family of functions) are case insensitive